linux-kernel - RE: [PATCH -v2 -mm] add extra free kbytes tunable

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Message-ID: <65795E11DBF1E645A09CEC7EAEE94B9CB516D055@USINDEVS02.corp.hds.com>
Date:	Wed, 12 Oct 2011 17:08:57 -0400
From:	Satoru Moriya <satoru.moriya@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Satoru Moriya <smoriya@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"lwoodman@...hat.com" <lwoodman@...hat.com>,
	Seiji Aguchi <saguchi@...hat.com>,
	"hughd@...gle.com" <hughd@...gle.com>,
	"hannes@...xchg.org" <hannes@...xchg.org>
Subject: RE: [PATCH -v2 -mm] add extra free kbytes tunable

On 10/11/2011 04:54 PM, Andrew Morton wrote:
> On Tue, 11 Oct 2011 16:23:22 -0400
> Satoru Moriya <satoru.moriya@....com> wrote:
>
>> Also, if we increase the free-page reserves a.k.a min_free_kbytes, 
>> the possibility of direct reclaim on other workloads increases.
>> I think it's a bad side effect.
> 
> extra_free_kbytes has the same side-effect.

I don't think so. If we make low watermark bigger to increase
free-page reserves by extra_free_kbytes, the possibility of
direct reclaim on other workload does not increase directly
because min watermark is not changed. 
Of course, as David pointed out, other workloads may incur
a regression because kswapd uses more cpu time.

Thanks,
Satoru
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